Waterflooding extraction is the general oilfield extraction method in China, but long-term use of waterflooding extraction causes the worsening of stratigraphic heterogeneity, and further causes the acceleration of water production increase during the mid and late oilfield extraction period, low water displacing efficiency or invalid circulating as well as the incapability to extract large amount of oil stayed in stratum. Therefore, how to apply potential tapping of remaining oil is crucial and significant to the stable and increasing yield of the mid to late water flooding extraction in oilfield. Improving the swept volume of flooding agent and displacing efficiency are two approaches for controlling water and stabilizing oil in oilfields nowadays, and chemical combination flooding technologies mainly comprising polymer/surfactant binary combination flooding and polymer/surfactant/alkali ternary combination flooding are the most important technical means for remaining oil potential tapping, also, success have been achieved from on-site application of such chemical combination flooding technologies. The main function of polymer in compound flooding is to increase the viscosity of flooding fluid to expand its swept volume, while the main roles of surfactant and alkali are to decrease the oil/water interface tension, to emulsified crude oil and to change the rock wettability for improving the displacing efficiency, and eventually achieving the deep potential tapping of residual oil. However, there are some problems of chemical combination flooding technologies in on-site application: such as, in polymer/surfactant based binary combination flooding method, the polymer are influenced by the shearing of mechanical equipment and formation porous as well as the physicochemical properties of the stratum, which causes a significant decrease of polymer viscosity and weakening of mobility control ability; in polymer/surfactant/alkali ternary combination flooding, the addition of alkali greatly improves the effect of ternary combination flooding, but the existence of alkali will cause scaling in shaft and injury to stratum, also bring difficulties to demulsification of the subsequent produced liquid.
The key of combination flooding technology is how to select reasonable polymer and high-efficient surfactant, while the adverse effect of alkali can be minimized and combination flooding effect can be achieved. CN102504794A discloses a hydrophobic associated polymer-mixed surfactant binary combination flooding system used for tertiary oil recovery, which consists of hydrophobic associated polymer, petroleum sulfonate, n-pentanol, dodecyl betaine and water for the rest. This combination flooding system can decrease oil/water interface tension for 10−3 mN/m, and improve the recovery efficiency by more than 20%. However, the components of mixed surfactant are relatively complicated, the mobility control ability of polymer in the combination flooding is relatively weak, especially in the subsequent flooding period the injection pressure decreases fast, and the flooding agent is easy to escape to nearby oil well, which significantly limit the flooding effect of flooding agent, decrease the use value of flooding agent and is difficult to get a long-term development effect.
To improve mobility control ability of the polymer in the polymer flooding or the combination flooding and to overcome the uncontrollable influence of stratum conditions, the colloidal dispersion gel (CDG), pre-performed particle gel (PPG) and the dispersed-particle gel (DPG) profile control and flooding technologies are developed. However, the colloidal dispersion gel (CDG) are influenced by the shearing of mechanical equipment and formation porous as well as the physicochemical properties of the stratum, which causes the uncontrollable of the gelation time of gel, the gel strength and the entering depth into stratum difficult. The injectivity and selectivity of pre-performed particle gel (PPG) is worse. Considering the deficiency of the prior art, CN102936490A discloses a preparation method of an environmentally friendly multi-scale zirconium gel particles. This preparation method is simple but effective, and the zirconium gel particles prepared is not affected by the uncontrollable formation condition during the gelation reaction which may satisfy the need for large-scale industrial production, additionally, the zirconium gel particles is environmentally friendly. Because of its particle scale, the zirconium gel particles of nanometer-scale, micron-scale and millimeter-scale obtained by using this method can enter into the deep stratum, then aggregates and strands in the deep stratum, in order to effectively adjust the water injection profile in stratum. In addition, the mobility control ability of the zirconium gel dispersion is better, which will eventually switch the subsequent waterflooding to low permeability layer and expand the coverage of subsequent waterflooding. However, this method concentrates on achieving high oil recovery from expanding the coverage of subsequent fluid, but takes no account of how to improve displacing efficiency of flooding agent.
In order to maximize the oil recovery, a new kind of displacement combination flooding system needs to be developed which not only can increase displacement efficiency, but also expand the swept volume.